FIG. 1 shows a prior art regulated inductive DC/DC converter producing an output voltage VS from an energy source VBAT and comprising:                a selector switch 10 comprising a first input coupled to the energy source VBAT, a second input coupled to a ground GND, and an output coupled to a first terminal of an inductor L, a second terminal of which is coupled to an output terminal S of the converter to which a load CH and a capacitor C are parallel-coupled,        a regulator 20 to produce a control signal COM as a function of a result of a comparison of an output voltage VS with a reference voltage VREF,        a control circuit 25 to couple the output of the selector switch 10 to the first or second input of the selector switch, as a function of the control signal COM.        
The selector switch 10 comprises in practice two switches T1, T2 series-coupled between the first input and the second input of the selector switch, a common point of the switches T1, T2 forming the output of the selector switch.
From the signal COM received from the regulator 20, the control circuit 25 produces two control signals PWM1, PWM2 suited to controlling the switches T1, T2 of the selector switch so as to impose the voltage VBAT on the first terminal of the inductor for a time T0 and impose the voltage GND on the first terminal of the inductor for a time T-T0. The inductor L and the capacitor C thus store energy during the time T0 and restore it during the time T-T0. The current given by the inductor to the load is proportional to the cyclical ratio T0/T. The capacitor C is used to maintain the output voltage VS at a constant level.
For the control of the selector switch, the regulator uses a pulse-width modulation (PWM) which causes the cyclical ratio T0/T to vary. If the output voltage is lower than the reference voltage, the cyclical ratio increases. Inversely, if the output voltage is greater than the reference voltage, the cyclical ratio falls.
A converter of this kind works in a continuous mode of operation when the current flowing in the inductor L is never cancelled out during a period T. This is the case especially when the current given to the load is substantial or when the quantity of energy given to the load is substantial. The converter works in a discontinuous mode of conduction when the current in the inductor gets cancelled out during a part of the period T. This is the case especially when the quantity of energy required by the load is low enough to be transmitted to the load in less than one change-over switching period T.
A converter such as this has high efficiency, of the order of 90 to 98%, especially when the output current given to the load is in a range of about 30% to 70% of a maximum current IM for which the converter has been sized.
However, the efficiency of the converter may fall sharply when the output current diminishes and becomes low or very low when it is of the order of some milliamperes. The efficiency of the converter is thus, for example, of the order of 30% to 40% when the output current is below 30% of the maximum current IM. This is due to the fact that the switching losses in the selector switch become non-negligible relative to the energy given to the load with low output current.